Note 2 - Investment Securities - Available-for-sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Securities available-for-sale, amortized cost	$ 1,238,249	$ 1,297,977
Securities available-for-sale, unrealized gains	222	349
Securities available-for-sale, unrealized losses	(145,747)	(153,709)
Securities available-for-sale, fair value	1,092,724	1,144,617
US Treasury Securities and US Government Agencies Debt Securities [Member]
Securities available-for-sale, amortized cost	122,927	122,966
Securities available-for-sale, unrealized gains	0	0
Securities available-for-sale, unrealized losses	(6,710)	(7,927)
Securities available-for-sale, fair value	116,217	115,039
US Government-sponsored Enterprises Debt Securities [Member]
Securities available-for-sale, amortized cost	139,479	149,773
Securities available-for-sale, unrealized gains	199	290
Securities available-for-sale, unrealized losses	(6,103)	(6,437)
Securities available-for-sale, fair value	133,575	143,626
Mortgage-Backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities available-for-sale, amortized cost	829,867	874,265
Securities available-for-sale, unrealized gains	22	58
Securities available-for-sale, unrealized losses	(117,177)	(121,585)
Securities available-for-sale, fair value	712,712	752,738
US States and Political Subdivisions Debt Securities [Member]
Securities available-for-sale, amortized cost	142,086	145,016
Securities available-for-sale, unrealized gains	1	1
Securities available-for-sale, unrealized losses	(15,307)	(17,418)
Securities available-for-sale, fair value	126,780	127,599
Other Debt Obligations [Member]
Securities available-for-sale, amortized cost	3,890	5,957
Securities available-for-sale, unrealized gains	0	0
Securities available-for-sale, unrealized losses	(450)	(342)
Securities available-for-sale, fair value	$ 3,440	$ 5,615